A large number of normal immune responses require the participation of T-cells. The proliferation of T-cells to sufficient numbers to assume an effective role in immune responses is controlled by the presence of interleukin-2 (hereinafter "IL-2"), Gillis and Smith, 28 Nature 154 (1977). Although the mechanism by which IL-2 controls the growth of T-cells is not fully understood, it is known that IL-2 acts on T-cells via a specific, high-affinity, plasma membrane receptor, i.e., IL-2 receptor. Also, in order to continue to divide, IL-2 dependent T-cells must express the IL-2 receptor and the IL-2 must bind to a portion of the IL-2 receptor, Robb et al., 154 J. Exp. Med. 1455 (1981). A more complete knowledge of the biochemistry of the IL-2 receptor would foster a better understanding of the interaction between IL-2 and T-cells. To date, this has been hampered, at least in part, by the unavailability of sufficient amounts of IL-2 receptor in purified form.
Leonard et al., 300 Nature (London) 267 (November 1982), reported employing a murine monoclonal antibody, designated as anti-Tac, to significantly block the binding of radiolabelled IL-2 to the human lymphoma T-cell line, HUT-102. This antibody resulted from the immunization of mice with long term cultures of human T-cells. The anti-Tac antibody was reported as binding both to a glyco-protein having a molecular weight of about 47,000-53,000 daltons and also to proteins having molecular weights of about 113,000 and 180,000 daltons. Leonard et al. hypothesized, but did not establish, that the cell surface determinant (i.e., the 47,000-53,000 molecular weight protein) to which the anti-Tac antibody bounded to was the IL-2 receptor.
Robb and Green, 158 J. Exp. Med. 1332 (1983), reported employing the anti-Tac antibody in conjunction with mitogen-activated normal lymphocytes to immunoprecipitate a protein having a molecular weight of about 52,000-57,000 daltons. They found that this same protein also bound to IL-2. These researchers opined that this reactive molecule contained the binding site for IL-2 for normal lymphocytes.
Leonard et al., 80 Proc. Natl. Acad. Sci. (USA) 6957 (1983) observed that receptors recognized by anti-Tac antibody on HUT-102 cells and on phytohemaggelutinin-activated normal T-cells appear to be larger on reducing gels than on nonreducing gels, thus suggesting the presence of intrachain disulfide bonds. Also, the HUT-102 cell receptor was reported to exhibit an isoelectric point of from 5.5 to 6.0. From post-translational studies, Leonard et al. suggested that the HUT-102 receptor is composed of a peptide backbone of 33,000 daltons that is initially glycosylated by an N-linked mechanism to achieve a 35,000-37,000 daltons doublet and then glycosylated by an O-linked mechanism to increase the weight of the molecule by about 13,000-15,000 daltons. Although the researchers stated that their studies "suggested" that the HUT-102 cell receptor recognized by the anti-Tac antibody is the human receptor for IL-2, they admitted that actual proof would require purifying the receptor, which prior to the making of the present invention had not been accomplished.
Recombinant DNA techniques have been developed for economically producing a desired protein once the gene coding for protein has been isolated and identified. A discussion of such recombinant DNA techniques for protein production is set forth in the editorial and supporting papers in Vol. 196 of Science (April, 1977). However, to take advantage of the recombinant DNA techniques discussed in these references, the gene coding for the IL-2 receptor must first be isolated.